If a motor vehicle has an asymmetric load on its chassis, for instance, if the boot or trunk of the vehicle is heavily laden, then the vehicle will pitch out of the horizontal plane. Since vehicular headlights are calibrated to a given load which is deemed horizontal, any pitch of the vehicle will mean that a light emission angle from the vehicle will be skewed, which can result in glare to oncoming motorists, and/or incorrect illumination of the road surface. This is of particular concern in poor lighting conditions, such as at night or in foggy conditions.
Actuation units are known which are capable of altering the light emission angle of the headlamps in response to the asymmetric load. The pitch of the vehicle is determined in such systems by mounting a plurality of pitch sensors about the chassis of the vehicle, typically at or adjacent to the wheels, and then calculating a vertical displacement between the various sensors so as to determine an overall pitch of the vehicle.
Such systems require a plurality of pitch sensors which may need optical access to the road below and/or be otherwise exposed to the road surface below, for example, where the pitch sensors are formed as potentiometers mounted on the axles of the vehicle. This places various restrictions on the pitch sensors; firstly, the sensors must all be in communication, typically wired communication, with a controller which is able to calculate the pitch of the vehicle based on the output of the pitch sensors; and the pitch sensors are unable to be enclosed securely due to the requirements for exposure.
The positioning of the sensors about the chassis requires that a plurality of wires must be provided along the chassis. This wiring is prone to failure, particularly over extended periods of use and/or in harsh working conditions, which can result in failure of the actuator system as a whole. Furthermore, the requirements for exposure also mean that shielding is required for the pitch sensors, so as to prevent accidental damage from, for example, debris on the road surface.